SEARCH · PubMed Health

Results for “Pyramidal Tracts”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 973 records · Page 54Linked to original sources

PubMed2003

Corticospinal volleys evoked by transcranial stimulation of the brain in conscious humans.

The direct recording in conscious humans of corticospinal volleys evoked by different magnetic and electric techniques of transcranial stimulation demonstrates that it is possible to activate neurones of the motor cortex in several different ways. Lateral electrical stimulation of the motor cortex preferentially activates the axons of corticospinal neurones in the subcortical white matter, and evokes a D-wave in pyramidal tract. The way of activation of corticospinal neurones using magnetic stimulation depends on the direction of the electrical current induced in the brain and on the shape of the coil. Monophasic magnetic stimulation with a focal figure-of-eight coil inducing posterior-anterior current in the brain activates corticospinal neurones trans-synaptically recruiting an 11-wave, with later I-waves appearing in sequence at higher intensities and a D-wave at very high intensities. If the induced current is rotated to the anterior-posterior direction late I-waves are preferentially recruited and when a D-wave is recruited, it has a later onset than the electrical D-wave, suggesting an activation nearer the cell body of the pyramidal neurones. A latero-medial induced current activates both corticospinal axons at the same point as electrical stimulation evoking a D wave and cortico-cortical axons evoking I-waves. A nonfocal large circular coil centered at the vertex is capable of activating pyramidal neurones both at the initial segment and trans-synaptically evoking a D wave with a longer latency than the electrical D-wave and I-waves. Using a biphasic magnetic stimulation, both phases of the biphasic pulse are capable of activating descending motor output and the pattern of recruitment of descending activity depends on the intensity of the stimulus and the relative threshold of each volley to each direction of current flow.

Consciousness↗

PubMed1983

Pyramidal input to the intracerebellar nuclei of the cat.

In unanesthetized cats it has been found that pyramidal volleys elicited upon medullary pyramidal tract stimulation were capable of modifying the discharge of 41% of intracerebellar nuclear cells, via pontocerebellar systems impinging predominantly on the lateral cerebellar cortex. The incidence of responsive cells was 80% in the dentate nucleus compared with 10% in the fastigial nucleus, 11% in the anterior and 12% in the posterior division of the interpositus nucleus. The response was in 59% of the cases excitation followed by inhibition, in 30% of the cases a pure excitation and in 11% of the cases a pure inhibition. Excitation, pure or followed by inhibition, had a mean latency of 5.78 ms and a mean duration of 12.21 ms, while inhibition displayed a mean latency of 9.03 ms and a mean duration of 34.64 ms. The possible functional significance of the pyramidal input to the lateral cerebellum is briefly discussed in relation to a possible convergence of pyramidal and associative impulses in single cerebellar neurons.

Animals↗

PubMed1993

[A case of motor neuropathy with pyramidal sign due to prolonged administration of high dose of pancuronium bromide (Myoblock)].

We reported a case of motor neuropathy with pyramidal sign following prolonged administration of a high dose of muscle relaxant, pancuronium bromide (Myoblock). A 40-year-old male was admitted to our hospital with acute episode of pancreatitis. He was treated with artificial ventilation and Myoblock to manage delirious state, disseminated intravascular coagulation and multiple organ failure. Total dose of 823 mg (24 mg/day) of Myoblock was given intravenously over 36 days. After Myoblock was discontinued, he regained his consciousness and marked muscle weakness with atrophy was noted in both limbs, more severe in distal lower limbs, without any noticeable sensory and sphincter disturbances. Motor nerve conduction studies showed normal nerve conduction velocities with markedly decreased amplitude of compound muscle action potentials. Repetitive nerve stimulation studies revealed decrement response after tetanic stimulation, which disappeared later. Needle EMG showed active denervation potentials and marked polyphasic motor unit potentials. Muscle biopsy revealed neurogenic muscle atrophy with fragmented acetylcholine esterase-positive postsynaptic sites. Sural nerve biopsy showed slight to moderate degree of axonal degeneration of myelinated fibers. Clinical, electrophysiological, and pathological studies above indicated that the main affected sites were neuromuscular junctions including the terminal twigs of motor neurones and postsynaptic membrane, and pyramidal tracts, predominant in lower limbs. About one month after the recognition of the muscle weakness, his muscle strength improved gradually, however, spasticity with hyperreflexia and pathologic reflexes of both legs were found, and became more prominent thereafter. Intensive physiotherapy and rehabilitation led improvement to the point that he became able to ambulate with walking-aids about 7 months later, but marked spasticity persisted.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗

PubMed2002

[Vacuolar leucoencephalopathy induced by heroin: 4 cases].

We report 4 cases of toxic leucoencephalopathy after heroin inhalation. The clinical features, which usually occur some days or even longer after the last heroin consumption, are dominated by a cerebellar syndrome. The cerebellar hemispheres are almost always affected; the cerebral hemispheres, the cerebellar peduncles and the pyramidal tract may be affected. Vacuolar demyelination is the morphological substract of the lesions, which are symmmetrical, not contrast enhancing, hypodense on CT scan and hyperintense on T2-weighted MRI. The pathophysiology is unknown and seems different from post-anoxic leucoencephalopathy. The disease is usually progressive leading sometimes to death, but some cases show slow recovery.

Administration, Inhalation↗

PubMed1993

Alterations of motor evoked potentials by thalamotomy.

To evaluate the effect of stereotactic thalamotomy on the function of the corticospinal tract, we studied motor evoked potentials (MEPs) recorded by surface electromyography (EMG) in the left extensor carpi radialis (ECR) and flexor carpi radialis (FCR) with magnetic stimulation of the contralateral motor cortex in a 43-year-old patient with a severe postural and resting tremor of the left hand. The patient was diagnosed eight years previously with left hemiparkinsonism. The tremor was unresponsive to various medications. After thalamotomy the tremor had disappeared, confirmed by EMG studies. MEP latencies at rest were normal and did not change after thalamotomy. Volitional contraction of either ECR or FCR shortened the latency of the corresponding MEP before and after thalamotomy. However, before thalamotomy responses at rest were less well synchronized and followed by EMG silence with subsequent long duration tonic after discharges. Furthermore, during voluntary contraction the responses only slightly enhanced. After surgery MEPs at rest in both muscles were more synchronized and after-discharges had disappeared. Moreover, with volitional contraction of either ECR of FCR, the MEPs enhanced more dramatically. The silent periods (SPs) following the MEP during sustained voluntary contraction were longer after thalamotomy. The consistent MEP latencies suggest that the conduction of the pyramidal tract is unaffected by thalamotomy. The better synchronized responses, the alleviation of after-discharges and the longer SPs in this patient with hemiparkinsonism following thalamotomy suggest an improved sensorimotor integration, which may be the result of a reduced thalamic input onto suprasegmental levels.

Adult↗

PubMed1983

Gerstmann-Sträussler-Scheinker's disease.

Findings are reported in three members of a Japanese family with a chronic familial disease characterized by signs of marked cerebellar dysfunction, mild pyramidal and extrapyramidal dysfunction, and loss or decrease of the knee and ankle jerks. Although the clinical features suggested olivopontocerebellar atrophy, postmortem study of one patient with obvious dementia revealed massive multiform plaques of Kuru type as well as multicentric, senile, and primitive types throughout the central nervous system, most prominent in the cerebellar and cerebral cortices and caudate nucleus. There was degeneration of the spinocerebellar and pyramidal tracts, posterior columns, superior cerebellar peduncles, cerebellar cortex, dentate nucleus, and vestibular nuclei as well as gliosis of the inferior colliculus and cerebellar foliar white matter. There were no cerebral spongiform changes, although slight spongy alteration without glial reaction was present. The clinical and neuropathological characteristics were consistent with those reported as Gerstmann-Sträussler-Scheinker's disease in an Austrian family.

Aged↗

PubMed1983

[Classification of amyotrophic lateral sclerosis (clinico-electromyographic study)].

On the basis of the clinical electromyographic examination of 117 patients with lateral amyotrophic sclerosis, the relationship was ascertained between the manifestations of this illness and the primary localization of amyotrophies in the distal or proximal regions of the extremities. The first group was characterized by rapid generalization of the pathological process and by the presence of marked symptoms of the involvement of the segmento-nuclear motoneurons and the pyramidal tracts whilst the second group largely manifested impairment of the anterior cornual motor cells and the spinal localization of the process throughout the course of the disease. It is suggested that cervicothoracic and lumbosacral forms of the illness be subdivided into distinctive variants in relation to the primary localization of amyotrophies in the distal or proximal regions of the extremities.

Adolescent↗

PubMed2003

Optimization of diffusion-tensor MR imaging data acquisition parameters for brain fiber tracking using parallel imaging at 3 T.

The purpose of this study was to optimize the parameters of diffusion-tensor magnetic resonance imaging (DT MRI) for brain fiber tracking using a slice thickness of 2 mm, a resolution advantage allowed by the high signal-to-noise ratio at 3 T, combined with an 8-channel phased-array head coil. The b-factor, number of motion probing gradient (MPG) directions, and number of averages were varied, and the results of brain fiber tracking for the pyramidal tract and trigeminal nerve were compared qualitatively and quantitatively. The DT MRI data sufficient for brain fiber tracking in healthy subjects can be obtained in <2 min with a 2-mm slice thickness, 700-s/mm2 b-factor, 6 MPG directions, and no averaging (number of averages=1).

Adult↗

PubMed1979

On a possible neural mechanism underlying a finding by Evarts and Fromm.

A finding by Evarts and Fromm [1] that the number of unit firings in certain pyramidal-tract neurons is very large for very small, but precise, movements suggests that the mathematical Law of Large Numbers may be operating here. According to this law, under suitable conditions the average of a large number of variables is very precisely defined--its deviation from its ideal value being less the larger the number of variables. Such an algorithm operating in the nervous system might generate precision of muscle control from the frequency of firing of neutrons belonging to a certain neuron system.

Models, Neurological↗

PubMed1996

The central nervous system in Tay syndrome.

Trichothiodystrophy (brittle sulfur-deficient hair) is a marker for several autosomal recessive neurocutaneous syndromes with neurological manifestations and mental retardation. In Tay syndrome, the trichothiodystrophy is accompanied by congenital ichthyosis, short stature, delayed physical and mental development and pyramidal tract signs with increase in muscular tone and brisk tendon reflexes. The pathogenesis of these neurological manifestations is not fully elucidated. We present a case of Tay syndrome in which a cranial MRI revealed an almost total lack of myelin within the cerebral hemispheres and a patchy hypomyelination of the cerebellum. In accordance, a strongly prolonged visual evoked response pointed to a dysfunction of the white matter in Tay syndrome.

Ataxia↗

PubMed1994

Neuronal activity in normal and deafferented forelimb somatosensory cortex of the awake cat.

Three hundred and seventy-three neurons were recorded from the forelimb representation in the primary somatosensory cortex of unanesthetized, quietly resting adult cats. Of these, 177 were studied from 2 days to 3 weeks after transection of the radial, median and ulnar nerves. Following deafferentation the proportion of cells without receptive fields increased from 24 to 82%, however, the average rate of spontaneous activity did not change nor did the probability of encountering a neuron with a receptive field as a function of depth. Receptive field sizes increased dramatically following deafferentation and the response changed from a reliable short-latency, brisk discharge to one that did not occur on every stimulus. After deafferentation the edges of the receptive field often could not be defined accurately. Spontaneous activity in 31% (n = 47) of the neurons from deprived cortex could be modulated by manipulations of the body but these changes were sufficiently slow and ill-defined that they were not classified as a receptive field. In some cases, manipulation of the body gradually reduced the discharge rate. This slow decline in activity was different from the abrupt inhibition of spontaneous activity elicited by somatic stimuli in another class of cells (n = 18). In other cases the manipulation produced a gradual increase in the discharge rate. After deafferentation antidromically identified corticothalamic and pyramidal tract neurons did not display behaviors different from their counterparts in normal cortex. However, the mean latency for synaptic activation from the ventroposterior thalamus increased from 2.7 ms to 4.6 ms. The lost forelimb receptive fields were rarely replaced by inputs from adjacent body parts over the two-week duration of this study. Most responses to somatic stimuli obtained from cortical neurons in the deafferented cortex were clearly abnormal.

Afferent Pathways↗

PubMed1991

[Rearrangement of the efferent activity of a locomotor generator under electric activation of descending systems in immobilized cats].

Rearrangement of the locomotor generator activity evoked by phasic electrical stimulation of different descending systems has been investigated on decerebrated immobilized cats. The rearrangement heavily depends on the stimulation phase. A maximal increase of the locomotor cycle duration by electrical stimulation of the Deiters nucleus takes place in the end of an "extensor" phase. Stimulation of the Deiters nucleus during the flexor phase decreases the locomotor cycle duration. A maximal increase of the locomotor cycle duration by electrical stimulation of the red nucleus, pyramidal tract and reticular gigantocellular nucleus takes place in the first half of a "flexor" phase. Electrical activation of these descending pathways during the flexor phase promotes an increase in intensity of this phase and a decrease in intensity of the "extensor" phase. Electrical activation of the Deiters nucleus increases intensity of the extensor phase and decreases that of the "flexor" phase. Possible principles of the suprasegmental correction of the locomotor generator activity are discussed.

Animals↗

PubMed1982

Rapid anterograde movement of the fluorescent tracer Fast Blue: a new method for tracing central connections.

Following Fast Blue application to the frontoparietal areas of the cat cerebral cortex on one side, labeled axons, axon collaterals and terminal arborizations could be traced through the 'pyramidal tract' fiber system to all its main areas of termination. Prominent Fast Blue-labeling of axon collaterals and terminals was found in the red nucleus, the pontine nuclei and the cervical level of the spinal gray, as early as 48 h survival time. These observations show that Fast Blue is effectively moved anterogradely through axons and that it can be used as an anterograde tracer to label axonal efferent connections.

Animals↗

PubMed1984

Electrophysiological study on the corticoreticular projection neurons of the cat.

Thirty-two motor cortical neurons of the cat which project on medullary reticular formation (RF) were electrophysiologically classified into 3 groups, i.e., 22 slow PT-RF neurons (collateral projections to RF from slow pyramidal tract (PT) neurons), 6 fast PT-RF neurons (those from fast PT neurons) and 4 RF (non-PT) neurons without any relation to PT neurons. Firings of slow PT-RF and RF (non-PT) neurons elicited by thalamic stimulation showed close correlation to the surface negative component of cortical evoked potentials. It was suggested that activities of these neurons are controlled mainly by excitatory thalamic inputs onto the distal and superficial part of their apical dendrites.

Animals↗

PubMed1975

Undershoots following stimulus-induced rises of extracellular potassium concentration in cerebral cortex of cat.

Extracellular potassium activity (ak) was recorded with potassium-sensitive electrodes in the sensorimotor cortex of cats. Resting activity was 2.8--3.4 mEquiv/l. Electric stimulation of the cortical surface and the nucleus ventroposterolateralis of the thalamus brought about an increase in aK followed by an undershoot and return to normal value. The lowest observed value of aK was 2.1 mEquiv./l. Size and duration (range 0.5--4 min) of the undershoots of aK increased with increasing peak amplitudes of the preceding rise in aK. Following the rise in aK, a period of reduced neuronal activity was observed which usually shorter lasting than the decrease in extracellular aK. An undershoot of aK and a concomitant reduction of neuronal discharge frequency can also occur in immediate response to antidromic stimulation of the pyramidal tract. To compare the K+ redistribution at normal and reduced levels of aK electrophoretic K+ signals were produced with constant current pulses from a proximate KCl-filled capillary. Both amplitudes and half times of decay of these K+ signals were found to decrease during the phase of poststimulatory undershoot in aK (19 and 23% respectively). It is suggested that an activated reuptake of potassium contributes to the decrease in extracellular aK in addition to inhibitory processes.

Animals↗

PubMed2001

[Clinical and pathological characteristics of heroin spongiform leukoencephalopathy in China].

OBJECTIVE: To observe the clinical, image and pathological characteristics of Heroin Spongiform Leukoencephalopathy(HSLE). METHODS: Clinical, CT and MRI analysis of 28 cases, brain autopsies of 2 cases and brain biopsies of 8 cases with HE, Loyez and Congo Red staining and observation through electron microscope. RESULTS: The clinic, image and pathologic characteristics of HSLE: (1) the history of inhalation of heated heroin vapor; (2) among 28 cases with HSLE, recurrence of HSLE was found in 17 cases during the abstinence, in 8 cases 1-2 month after abstinence, in 2 cases 4 month after abstinence and in 1 case after inhaling large amount of heroin; (3) the majority of cases were described with the acute onset characterized by cerebellar signs; (4) pyramidal tract lesion was frequently involved, but sensory system usually remained normal; (5) CSF test was normal; (6) CT and MRI revealed extensive symmetric white matter lesions in cerebra and cerebellum; (7) spongiform vacuoles degeneration of white matter was the main morphological change. CONCLUSIONS: Spongiform leukoencephalopathy may be considered if a patient who had a history of inhaling heated heroin vapor showed acute cerebellar signs. Spongiform vacuoles degeneration of cerebral white matter was the main pathological change.

Adult↗

PubMed1978

Propriospinal neurones as a relay system for transmission of cortico-spinal influences.

1. Synaptic organization and transmission have been studied in the lateral group of short propriospinal neurones of the lumbar and cervical regions of the cat spinal cord. Special attention was paid to their role in the transmission of cortico-spinal volleys. 2. The majority of these neurones are mono- or oligosynaptically excited after pyramidal tract stimulation. Convergence of excitatory actions from rubrospinal and lateral reticulospinal tracts was typical for these cells. Neurones with relatively low-level and delayed effects from segmental afferents are frequent in this population. 3. Temporal summation is important for the transmission of descending vlleys through these neurones. Mutual excitatory and recurrent inhibitory connections are supposed to play a substantial role in their function. 4. Possible participation of the short lateral propriospinal system in the transmission, transformation and re-distribution of corticofugal signals to the segmental spinal mechanisms is discussed.

Animals↗

PubMed1982

[Physiologic and pharmacologic differences in 3 types of pyramidal cells identified by antidromic stimulation in the primary somatosensory cortex of the rat].

The physiological and pharmacological properties of three types of pyramidal neurons (pyramidal tract neurons, cortico-thalamic neurons and commissural neurons) identified by electrical antidromic stimulation were studied in the first somatic sensory cortex of the Rat. The laminar distribution of these neurons (as determined through histological reconstruction of the electrode tracks), their axonal conduction velocity, their sensitivity to iontophoretically applied acetylcholine and their ability to be driven by the stimulation of a peripheral somatic receptive field were shown to be different in the three groups. Some hypotheses are discussed, which could explain such differences.

Acetylcholine↗